I use nothing but the black rubber on OE style covers.
Clean them up and straighten the sealing surface, then a 1/8 bead of RTV between the cover and gasket staying just on the inside of the bolt holes.
Then 1/8 bead of RTV down the center of the block side flattened and spread with a finger still going on the insides of the bolt holes.
Put it on and just lightly snug the bolts and let it sit for a few hours like that.
Then come back and tighten them down till you just see the rubber start to move around bolts and stop there.
I never have cover leaks doing it this way.
